The invention concerns an electronic-hydraulic control unit for an automatic transmission of a motor vehicle.
Automatic transmissions are being increasingly used in motor vehicles These can be transmissions having a continuously variable reduction step or multi-step transmissions which can be shifted under load or with traction interruption. To improve the ease when starting and changing the ratio to lower ratio steps in such transmissions, a hydrodynamic converter is often provided. Because of the unfavorable efficiency of the converter, a lock-up clutch is associated, which is engaged in the operating ranges when the converter is no longer needed. In an engaged state, the lock-up clutch transmits the power from an input shaft of the converter to an output shaft.
Associated with the transmission is an electronic hydraulic control unit which selects and activates an adequate ratio, according to the input, driving, and transmission parameters. In addition, the driver can choose, via a selector lever and/or program switch, a ratio step or a group of ratio steps, or driving programs. The control unit comprises one hydraulic unit, which in particular contains hydraulic valves, pressure regulators and sensors, and one electronic unit having electronic modules, which control electric or hydraulic actuators or regulators according to the measured or calculated parameters and/or stored characteristic fields. The hydraulic unit and the electronic unit are conveniently included in the control unit to form a functional unit.
Such control units have been disclosed in U.S. Pat. No. 4,271,728 and EP B1 0 697 080. Due to manufacturing tolerances of the individual elements of the control unit, the necessary working pressures for the hydraulic actuators of the automatic transmission are subject to corresponding tolerances. The tolerance chain which affects the working pressures includes, among others, the individual tolerances of the power regulators, the pressure regulators, the corresponding hydraulic valves, and the sensors required to detect these parameters.
The problem on which the invention is based is to reduce the tolerances of the control unit and, in particular, the scattered coordination of power delivery with working pressure.
According to the invention, pressure tolerances appearing in the operating range are detected by verifying characteristic lines. In addition, from the divergences in relation to a set characteristic line, a corresponding characteristic line correction is plotted and stored in memory of the electronic unit. Subject to the mating of hydraulics and software or hardware adjusted in each individual hydraulic control unit, it is possible by a measuring technique to fix the tolerances of the control unit over the operating range and compensate them by correction values in the electronic unit software. Since the sensors for detecting the parameters are also subject to tolerances, it is convenient that the tolerances of the sensor signals appearing in the operating range be likewise detected by verifying characteristic lines, and from the divergences relative to a set characteristic line, plot a corresponding characteristic line correction and store in memory of the electronic unit.